package com.paging.gridview.sample;

import android.os.Handler;
import android.os.Looper;
import android.util.Log;

import java.io.InterruptedIOException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.concurrent.Callable;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.Executor;
import java.util.concurrent.Executors;
import java.util.concurrent.FutureTask;


/**
 * A class similar but unrelated to android's {@link android.os.AsyncTask}.
 * <p/>
 * Unlike AsyncTask, this class properly propagates exceptions.
 * <p/>
 * If you're familiar with AsyncTask and are looking for {@link android.os.AsyncTask#doInBackground(Object[])},
 * we've named it {@link #call()} here to conform with java 1.5's {@link java.util.concurrent.Callable} interface.
 * <p/>
 * Current limitations: does not yet handle progress, although it shouldn't be
 * hard to add.
 * <p/>
 * If using your own executor, you must call future() to get a runnable you can execute.
 *
 * @param <ResultT>
 */
public abstract class SafeAsyncTask<ResultT> implements Callable<ResultT> {
	public static final int DEFAULT_POOL_SIZE = 25;
	protected static final Executor DEFAULT_EXECUTOR = Executors.newFixedThreadPool(DEFAULT_POOL_SIZE);

	protected Handler handler;
	protected Executor executor;
	protected StackTraceElement[] launchLocation;
	protected FutureTask<Void> future;


	/**
	 * Sets executor to Executors.newFixedThreadPool(DEFAULT_POOL_SIZE) and
	 * Handler to new Handler()
	 */
	public SafeAsyncTask() {
		this.executor = DEFAULT_EXECUTOR;
	}

	/**
	 * Sets executor to Executors.newFixedThreadPool(DEFAULT_POOL_SIZE)
	 */
	public SafeAsyncTask(Handler handler) {
		this.handler = handler;
		this.executor = DEFAULT_EXECUTOR;
	}

	/**
	 * Sets Handler to new Handler()
	 */
	public SafeAsyncTask(Executor executor) {
		this.executor = executor;
	}

	public SafeAsyncTask(Handler handler, Executor executor) {
		this.handler = handler;
		this.executor = executor;
	}


	public FutureTask<Void> future() {
		future = new FutureTask<Void>(newTask());
		return future;
	}

	public SafeAsyncTask<ResultT> executor(Executor executor) {
		this.executor = executor;
		return this;
	}

	public Executor executor() {
		return executor;
	}

	public SafeAsyncTask<ResultT> handler(Handler handler) {
		this.handler = handler;
		return this;
	}

	public Handler handler() {
		return handler;
	}

	public void execute() {
		execute(Thread.currentThread().getStackTrace());
	}

	protected void execute(StackTraceElement[] launchLocation) {
		this.launchLocation = launchLocation;
		executor.execute(future());
	}

	public boolean cancel(boolean mayInterruptIfRunning) {
		if (future == null) throw new UnsupportedOperationException("You cannot cancel this task before calling future()");

		return future.cancel(mayInterruptIfRunning);
	}


	/**
	 * @throws Exception, captured on passed to onException() if present.
	 */
	protected void onPreExecute() throws Exception {
	}

	/**
	 * @param t the result of {@link #call()}
	 * @throws Exception, captured on passed to onException() if present.
	 */
	@SuppressWarnings({"UnusedDeclaration"})
	protected void onSuccess(ResultT t) throws Exception {
	}

	/**
	 * Called when the thread has been interrupted, likely because
	 * the task was canceled.
	 * <p/>
	 * By default, calls {@link #onException(Exception)}, but this method
	 * may be overridden to handle interruptions differently than other
	 * exceptions.
	 *
	 * @param e an InterruptedException or InterruptedIOException
	 */
	protected void onInterrupted(Exception e) {
		onException(e);
	}

	/**
	 * Logs the exception as an Error by default, but this method may
	 * be overridden by subclasses.
	 *
	 * @param e the exception thrown from {@link #onPreExecute()}, {@link #call()}, or {@link #onSuccess(Object)}
	 * @throws RuntimeException, ignored
	 */
	protected void onException(Exception e) throws RuntimeException {
		onThrowable(e);
	}

	protected void onThrowable(Throwable t) throws RuntimeException {
		Log.e("roboguice", "Throwable caught during background processing", t);
	}

	/**
	 * @throws RuntimeException, ignored
	 */
	protected void onFinally() throws RuntimeException {
	}


	protected Task<ResultT> newTask() {
		return new Task<ResultT>(this);
	}


	public static class Task<ResultT> implements Callable<Void> {
		protected SafeAsyncTask<ResultT> parent;
		protected Handler handler;

		public Task(SafeAsyncTask<ResultT> parent) {
			this.parent = parent;
			this.handler = parent.handler != null ? parent.handler : new Handler(Looper.getMainLooper());
		}

		public Void call() throws Exception {
			try {
				doPreExecute();
				doSuccess(doCall());

			} catch (final Exception e) {
				try {
					doException(e);
				} catch (Exception f) {
					// logged but ignored
					Log.e("BACKGROUND_TASK", "Exception in", f);
				}

			} catch (final Throwable t) {
				try {
					doThrowable(t);
				} catch (Exception f) {
					// logged but ignored
					Log.e("BACKGROUND_TASK", "Exception in", f);
				}
			} finally {
				doFinally();
			}

			return null;
		}

		protected void doPreExecute() throws Exception {
			postToUiThreadAndWait(new Callable<Object>() {
				public Object call() throws Exception {
					parent.onPreExecute();
					return null;
				}
			});
		}

		protected ResultT doCall() throws Exception {
			return parent.call();
		}

		protected void doSuccess(final ResultT r) throws Exception {
			postToUiThreadAndWait(new Callable<Object>() {
				public Object call() throws Exception {
					parent.onSuccess(r);
					return null;
				}
			});
		}

		protected void doException(final Exception e) throws Exception {
			if (parent.launchLocation != null) {
				final ArrayList<StackTraceElement> stack = new ArrayList<StackTraceElement>(Arrays.asList(e.getStackTrace()));
				stack.addAll(Arrays.asList(parent.launchLocation));
				e.setStackTrace(stack.toArray(new StackTraceElement[stack.size()]));
			}
			postToUiThreadAndWait(new Callable<Object>() {
				public Object call() throws Exception {
					if (e instanceof InterruptedException || e instanceof InterruptedIOException) parent.onInterrupted(e);
					else parent.onException(e);
					return null;
				}
			});
		}

		protected void doThrowable(final Throwable e) throws Exception {
			if (parent.launchLocation != null) {
				final ArrayList<StackTraceElement> stack = new ArrayList<StackTraceElement>(Arrays.asList(e.getStackTrace()));
				stack.addAll(Arrays.asList(parent.launchLocation));
				e.setStackTrace(stack.toArray(new StackTraceElement[stack.size()]));
			}
			postToUiThreadAndWait(new Callable<Object>() {
				public Object call() throws Exception {
					parent.onThrowable(e);
					return null;
				}
			});
		}

		protected void doFinally() throws Exception {
			postToUiThreadAndWait(new Callable<Object>() {
				public Object call() throws Exception {
					parent.onFinally();
					return null;
				}
			});
		}


		/**
		 * Posts the specified runnable to the UI thread using a handler,
		 * and waits for operation to finish.  If there's an exception,
		 * it captures it and rethrows it.
		 *
		 * @param c the callable to post
		 * @throws Exception on error
		 */
		protected void postToUiThreadAndWait(final Callable c) throws Exception {
			final CountDownLatch latch = new CountDownLatch(1);
			final Exception[] exceptions = new Exception[1];

			// Execute onSuccess in the UI thread, but wait
			// for it to complete.
			// If it throws an exception, capture that exception
			// and rethrow it later.
			handler.post(new Runnable() {
				public void run() {
					try {
						c.call();
					} catch (Exception e) {
						exceptions[0] = e;
					} finally {
						latch.countDown();
					}
				}
			});

			// Wait for onSuccess to finish
			latch.await();

			if (exceptions[0] != null) throw exceptions[0];

		}

	}

}

